I needed to use OBS Studio to capture some video/audio from my desktop. On Mac OS X that in turn requires installing iShowU Audio Capture. That installation should be trivially easy, but it took me 2 weeks to work out how to get it installed, and a long email thread with the Shiny White Box support staff. The problem was the installation required that I give permission, but giving permission meant opening up the System Preferences to the Security pane and clicking on a button, and clicking on that button did not work. There is a fairly long list of possible suggestions that I have to share.

A "Kext" is a "Kernel Extension", meaning a piece of software that extends the functionality of the macOS Kernel. By the way, I'm still uncomfortable typing "macOS" after typing "Mac OS X" for the last 20 years. Apple... Why???

In the normal case, when a Kext installation requires permission a dialog is supposed to appear in front of the user. Clicking on the dialog is supposed to bring the user to the Security pane in the System Preferences. In the Security pane will be a message that an application by Such-And-So developer requires permission, and there is an Allow button. Clicking on the Allow button is supposed to bring up a dialog containing checkboxes, you tick off the checkboxes, click the OK button, and the system allows that Kext to function.

Here's a picture in case that paragraph of text did not make sense.

That's a nice and simple user experience. When it works. In my case, and the case of many others, clicking on the dang Allow button did nothing. The button would turn blue, but nothing would happen beyond this.

As always the recommendation to learn more is to enter relavent messages into your favorite search engine, like DuckDuckGo. Entering "Some system software was blocked from loading" into DuckDuckGo had some information but no quick fix.

Turns out that lots of people are having this issue and for many other applications.

The earliest suggestion was - make sure I'm doing this with a regular mouse or trackpad, not with a Wacom tablet, nor any other assistive device. In my case it is a MacBook Pro and I'm using the trackpad.

In the case of iShowU Audio Capture, there is a rigamarole required to carefully navigate the process. They supply an "Uninstall" application which lands in the Applications directory. So...

Run the Uninstall application

Reboot the system

Run the iShowU installer

Reboot the system

It's possible a system reboot will reset something and the Kext will load. This did not magically do the trick, but it's worth a try.

Debugging Kernel Extension installation quickly gets you into the geeky underbelly of the operating system. I was unable to find a nice GUI application to browse the Kext's and configure which does what and when.

This database is in a write-protected area of the macOS files. This database contains the flags as to which Kext's are allowed or not. Since the database is write-protected we must do something special to modify the database.

It's possible this sequence of steps is unnecessary for solving the problem. However for the purpose of definitively resetting the policies, it is necessary to boot into Recovery mode, start a Terminal window, and then modify the database. We restart in Recovery mode because doing so makes the database writable.

Make sure the iShowU application is uninstalled

Reboot -- hold down COMMAND-R until it starts booting

When it enters the macOS Install/Recovery window, click on the Utilities menu, then click on the Terminal choice

A terminal session with root privileges starts up ... so be careful

That login session is booted off a different file system than your normal macOS installation. Instead the normal macOS disk will be available as something like /Volumes/Macintosh SSD.

The bottom line is that there are many kinds of applications which can interfere with mouse input. Clicking on the Allow button fails because something interfered with the mouse click.

For example

Screen Sharing

Magic Perfs

Steer Mouse

xGestures

Slack .. Discord .. IntelliJ

..etc..

In other words there's a whole lotta things we might install that is about improving our experience of Mac OS X, and which could be mucking with mouse clicks.

In my case the definitive change happened after exiting Google Chrome. With Chrome running clicking on the Allow button did not work, and as soon as I made Chrome quit clicking on the Allow button started to work.

At that point, with Chrome shut down, I was able to use the Allow button as designed to approve all the Kext's, and then the iShowU device showed up in the Sound preferences as designed.

The discussion does talk about ways to use keyboard navigation to get keyboard focus on the Allow button - at which point it's possible to hit the Spacebar to trigger the button. I did not explore this but it is worth a try.

References

Namely, the Gatekeeper added in Mac OS X 10.7 had some changes in macOS High Sierra (10.13) that tightened down the process of installing Kext's. It also unfortunately contributed to the problems outlined on this page.